The present invention relates to controlled atmosphere rooms (CA rooms), and more particularly to monitor and control systems for CA rooms.
Perishable items, such as post-harvest fruits and vegetables, are often stored in a gastight storage facilities. The atmosphere in even a gastight storage space will vary over time as a result of various factors. One of the more important factors affecting atmosphere is fruit respiration. Fruit respiration can have a significant affect on the oxygen and carbon dioxide levels in a storage room. Fruit respiration is the natural ripening process that occurs in fruits and vegetable after harvest. Respiration is the uptake of oxygen and the discharge of carbon dioxide just like the human body would do while breathing. The post-harvest life of fruits and vegetable life can be prolonged for an extended marketing period when placed in gastight refrigerated storage rooms. Normal respiration would reduce the oxygen in the space and also elevate the carbon dioxide. Electronic analyzers are used to indicate the levels of the atmosphere in order for the operator to manage to a safe level to keep the fruit alive.
To provide improved storage, post-harvest commodities are often stored in controlled atmosphere rooms (“CA rooms”) where factors, such as temperature and atmospheric composition, can be controlled to extend the life of the items. CA rooms typically include systems for monitoring and controlling temperature and atmospheric conditions (e.g. oxygen, carbon dioxide and nitrogen levels) in a gastight space. The atmospheric control systems often operate by repeatedly sampling gas levels within the CA room and adding or removing gases to maintain the atmosphere at one or more desired setpoints. The setpoints are generally predetermined using knowledge gained from previous experience with the stored commodities. For example, a set of oxygen setpoints may be developed for a specific fruit to allow the system to adjust the oxygen levels in the atmosphere to follow a predetermined profile over time. Although past experience provides a good approximation, there are variations in commodities from year to year. These variations are typically significant enough that predetermined set points do not necessarily provide optimal control in all situations.
To address the potential limitations of predetermined setpoints, some CA rooms include a control system that operates to provide a dynamic controlled atmosphere (“DCA”). In the broadest sense, DCA technology provides a mechanism for dynamically monitoring and controlling the atmosphere in a CA room based not on predetermined setpoints, but rather on information derived on the fly through monitoring the response of the commodities to environmental changes. For example, the DCA control system may be configured to systematically change the absolute minimum level of oxygen in a gastight space available for the fruit in an effort to maintain just enough oxygen in the atmosphere for the commodities to stay alive. A reiterative process is beneficial because the minimum acceptable level will be ever changing over time depending on variety, age, temperature, etc. By dynamically maintaining minimal oxygen, the best postharvest life cycle of the stored commodity can be obtained.
The response of the stored commodity to changes can be determined by measuring characteristics affected by metabolic processes, such as ethanol production, chlorophyll fluorescence and respiration. Accordingly, DCA control methods may, for example, involve tests indicative of ethanol production, chlorophyll fluorescence and respiration. One way to understand the response of fruits and vegetables is to monitor the Respiration Quotient (“RQ”) as atmospheric changes are implemented by the DCA control system. The RQ is a number calculated from the actual change of oxygen and carbon dioxide in the gastight space. Normal natural respiration will reduce the oxygen and the carbon dioxide emitting from the fruit will raise the carbon dioxide in the space. Measuring RQ can be difficult in many CA rooms due to uncertainty of gastightness of the space and the adding of N2 gas to reduce oxygen or the removal of CO2 gas by outside scrubbers, which are normal processes of associated with running many CA rooms. The addition of outside influence gas will skew the natural respiration atmosphere shifting the true RQ.